Phytoliths analysis for the discrimination of Foxtail millet (Setaria italica) and Common millet (Panicum miliaceum).

Lu H, Zhang J, Wu N, Liu KB, Xu D, Li Q - PLoS ONE (2009)

Bottom Line:
Our research shows that five key diagnostic characteristics in phytolith morphology can be used to distinguish Foxtail millet from Common millet based on the presence of cross-shaped type, regularly arranged papillae, Omega-undulated type, endings structures of epidermal long cell, and surface ridgy line sculpture in the former species.We have established identification criteria that, when used together, give the only reliable way of distinguishing between Foxtail millet and Common millet species based on their phytoliths characteristics, thus making a methodological contribution to phytolith research.Our findings also have important implications in the fields of plant taxonomy, agricultural archaeology, and the culture history of ancient civilizations.

ABSTRACTFoxtail millet (Setaria italica) and Common millet (Panicum miliaceum) are the oldest domesticated dry farming crops in Eurasia. Identifying these two millets in the archaeobotanical remains are still problematic, especially because the millet grains preserve only when charred. Phytoliths analysis provides a viable method for identifying this important crop. However, to date, the identification of millet phytoliths has been questionable, because very little study has been done on their morphometry and taxonomy. Particularly, no clear diagnostic feature has been used to distinguish between Foxtail millet and Common millet. Here we examined the anatomy and silicon structure patterns in the glumes, lemmas, and paleas from the inflorescence bracts in 27 modern plants of Foxtail millet, Common millet, and closely related grasses, using light microscopy with phase-contrast and microscopic interferometer. Our research shows that five key diagnostic characteristics in phytolith morphology can be used to distinguish Foxtail millet from Common millet based on the presence of cross-shaped type, regularly arranged papillae, Omega-undulated type, endings structures of epidermal long cell, and surface ridgy line sculpture in the former species. We have established identification criteria that, when used together, give the only reliable way of distinguishing between Foxtail millet and Common millet species based on their phytoliths characteristics, thus making a methodological contribution to phytolith research. Our findings also have important implications in the fields of plant taxonomy, agricultural archaeology, and the culture history of ancient civilizations.

pone-0004448-g010: Bivariate biplot of R and W values of measurements from epidermal long cells of both species (P. miliaceum and S. italica).

Mentions:
We divide endings structures of epidermal long cell into Cross wavy type and Cross finger type based on characteristics of the dendriform epidermal long cell endings joining others (Figure 9). Cross wavy type, dendriform epidermal long cell endings joining others in a wavy pattern, is formed in the upper lemma and palea of S. italica. The average width of endings interdigitation of dendriform epidermal long cells is about 4.37±0.89 µm (N = 2774) (Figure 10) (Table 2). Cross finger type, dendriform epidermal long cell endings joining others in a deeply digital pattern, is formed in the upper lemma and palea of P. miliaceum. However, the average width of endings interdigitation of dendriform epidermal long cells is longer (8.95±2.02 µm, N = 3303) in the Cross finger type of P. miliaceum than that in S. italica. (Figure 10).

pone-0004448-g010: Bivariate biplot of R and W values of measurements from epidermal long cells of both species (P. miliaceum and S. italica).

Mentions:
We divide endings structures of epidermal long cell into Cross wavy type and Cross finger type based on characteristics of the dendriform epidermal long cell endings joining others (Figure 9). Cross wavy type, dendriform epidermal long cell endings joining others in a wavy pattern, is formed in the upper lemma and palea of S. italica. The average width of endings interdigitation of dendriform epidermal long cells is about 4.37±0.89 µm (N = 2774) (Figure 10) (Table 2). Cross finger type, dendriform epidermal long cell endings joining others in a deeply digital pattern, is formed in the upper lemma and palea of P. miliaceum. However, the average width of endings interdigitation of dendriform epidermal long cells is longer (8.95±2.02 µm, N = 3303) in the Cross finger type of P. miliaceum than that in S. italica. (Figure 10).

Bottom Line:
Our research shows that five key diagnostic characteristics in phytolith morphology can be used to distinguish Foxtail millet from Common millet based on the presence of cross-shaped type, regularly arranged papillae, Omega-undulated type, endings structures of epidermal long cell, and surface ridgy line sculpture in the former species.We have established identification criteria that, when used together, give the only reliable way of distinguishing between Foxtail millet and Common millet species based on their phytoliths characteristics, thus making a methodological contribution to phytolith research.Our findings also have important implications in the fields of plant taxonomy, agricultural archaeology, and the culture history of ancient civilizations.

ABSTRACTFoxtail millet (Setaria italica) and Common millet (Panicum miliaceum) are the oldest domesticated dry farming crops in Eurasia. Identifying these two millets in the archaeobotanical remains are still problematic, especially because the millet grains preserve only when charred. Phytoliths analysis provides a viable method for identifying this important crop. However, to date, the identification of millet phytoliths has been questionable, because very little study has been done on their morphometry and taxonomy. Particularly, no clear diagnostic feature has been used to distinguish between Foxtail millet and Common millet. Here we examined the anatomy and silicon structure patterns in the glumes, lemmas, and paleas from the inflorescence bracts in 27 modern plants of Foxtail millet, Common millet, and closely related grasses, using light microscopy with phase-contrast and microscopic interferometer. Our research shows that five key diagnostic characteristics in phytolith morphology can be used to distinguish Foxtail millet from Common millet based on the presence of cross-shaped type, regularly arranged papillae, Omega-undulated type, endings structures of epidermal long cell, and surface ridgy line sculpture in the former species. We have established identification criteria that, when used together, give the only reliable way of distinguishing between Foxtail millet and Common millet species based on their phytoliths characteristics, thus making a methodological contribution to phytolith research. Our findings also have important implications in the fields of plant taxonomy, agricultural archaeology, and the culture history of ancient civilizations.